Sensors are widely used in modern systems to measure or detect physical parameters, such as position, motion, force, acceleration, temperature, pressure, etc. While a variety of different sensor types exist for measuring these and other parameters, they all suffer from various limitations. For example, inexpensive low field sensors, such as those used in an electronic compass and other similar magnetic sensing applications, generally are Hall effect devices with flux concentrators or anisotropic magnetoresistance (AMR) based devices. In order to arrive at the required sensitivity and reasonable resistances that mesh well with CMOS, the sensing units of AMR sensors are generally on the order of square millimeters in size, while the auxiliary CMOS associated with hall effect sensors can similarly become large and expensive. For mobile applications, such AMR sensor configurations are too costly in terms of expense, circuit area, and power consumption.
Other types of sensors, such as magnetic tunnel junction (MTJ) sensors and giant magnetoresistance (GMR) sensors, have been used to provide smaller profile sensors, but such sensors have their own concerns, such as inadequate sensitivity and being effected by temperature changes. To address these concerns, MTJ, GMR, and AMR sensors have been employed in a Wheatstone bridge structure to increase sensitivity and to eliminate temperature dependent resistance changes. For minimal sensor size and cost, MTJ or GMR elements are preferred. Typically, a Wheatstone bridge structure uses magnetic shields to suppress the response of reference elements within the bridge so that only the sense elements (and hence the bridge) respond in a predetermined manner. However, the magnetic shields are thick and their fabrication requires carefully tuned NiFe seed and plating steps. Another drawback associated with magnetic shields arises when the shield retains a remnant field when exposed to a strong (˜5 kOe) magnetic field, since this remnant field can impair the low field measuring capabilities of the bridge structure. To prevent the use of magnetic shields, a Wheatstone bridge structure may include two opposite anti-ferromagnetic pinning directions for each sense axis, resulting in four different pinning directions which must be individually set for each wafer, very often requiring complex and unwieldy magnetization techniques.
A large external field, for example, the field to be measured, that is similar or greater in magnitude and opposite to the applied stabilization field can reduce, cancel, or reverse the stabilization field, resulting in increase in sensor noise and reset reliability problems, preventing an accurate measurement. Furthermore, a large external field opposite to the magnetic device reset direction effectively reverses the reset field and therefore the effectiveness of the reset operation.
Accordingly, it is desirable to provide a magnetoelectronic sensor fabrication method and layout having a high signal to noise ratio for measuring various physical parameters. There is also a need for a simple, rugged and reliable sensor that can be efficiently and inexpensively constructed as an integrated circuit structure for use in mobile applications. There is also a need for an improved magnetic field sensor and method to overcome the problems in the art, such as outlined above. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.